INHALANT EXPOSURE SYSTEM
An inhalant exposure unit and system that provides controlled flow of inhalant to an animal with a breathing system that provide controlled exposure of inhalant, minimized breathing of exhaled air and control of exhaust flow.
The invention provides a method and apparatus for controlled testing of single and multiple animals with selected inhalants. The invention provides for reduced rebreathing of exhaled breath.
BACKGROUND OF THE INVENTIONVarious inhalation exposure apparatus have been developed for providing controlled levels of inhalants to animals with the purpose of determining the impact on the animals. One of the primary considerations for inhalation exposure systems is that the inhaled materials be of the same concentration so that biological effects observed on the teat animals can be correlated and reproducibly obtained.
Recent world events have lead to increased concern of potential terrorist biological warfare attacks. One of the main biological warfare threats to humans is inhalational exposure to pathogenic bioaerosols. Examples of infectious diseases known to be caused by aerosolized bacteria are tuberculosis, legionellosis, and anthrax. Bacteria are single celled organisms with sizes from 0.3 to 10 um. Anthrax, a serious illness caused by the bacterium Bacillus anthracis, is considered one of the prototypical biological warfare biological warfare agents. One of the greatest bioaerosol threats is the inhalational exposure to Bacillus anthracis. The spore-forming ability makes Bacillus anthracis well suited for multiple delivery methods, which include liquid or dry agent disseminations. To protect against biological warfare attacks, various vaccines and post-exposure treatment approaches must be evaluated. To fully evaluate the efficacy of vaccines and therapeutics against bioaerosols of biological warfare agents, a well characterized and reproducible inhalant exposure system is needed. The inhalant exposure system and inhalant procedures, as much as possible, should follow Good Laboratory Practice regulations to support such studies for licensing of these products. The present invention includes the design, construction and initial characterization of an inhalation exposure system that can be used to challenge single to multiple animal models to support animal inhalation exposure testing of various products.
BRIEF DESCRIPTION OF THE INVENTIONA first broad embodiment of the invention includes an n inhalant exposure unit having a housing positioned around a central axis having an inlet end and an outlet end. A face plate is positioned vertically to the central axis at the outlet end of the housing but not in contact therewith. An annular outlet is formed by the spaced apart relationship of the outlet end and the face plate. The face plate has an axial opening for admitting at least a portion of an animal's head. In one embodiment the annular outlet is typically totally unimpeded by supports and the like so as to not impede the flow of inhalant and exhaled breath. In some embodiments, however, there may be one to several struts or supports such as those typically used in the art, that do not substantially interfere with the flow of inhalant and exhaled breath.
A yet further embodiment provides for an inhalant exposure unit having a housing 201 positioned around a central axis having an inlet end and an outlet end. At least a portion of the housing for this embodiment forms a truncated cone. The sides of the truncated cone form an angle θ with respect to the central axis. Typically the angle θ has a value of about 0° to about 60°. A face plate is positioned vertically to the central axis 103 at the outlet end of the housing but not in contact therewith. An annular outlet is formed by the spaced apart relationship of the outlet end of the truncated cone and the face plate. The face plate has an axial opening for admitting at least a portion of an animal's head. The benefits of the invention are obtained by having the flow of inhalant flow past the nostrils and/or mouth of the animal and sweep exhaled breath away from the animal's nose or mouth and into the annular outlet. The annular outlet is typically unimpeded by supports and the like so as to not impede the flow of inhalant and exhaled breath. In some embodiments, however, there may be one to several struts or supports such as those typically used in the art, that do not substantially interfere with the flow of inhalant and exhaled breath through the annular outlet. The conical shape the housing provides for enhanced flow of inhalant past the animal's head compared to the first embodiment that does not use a truncated cone. Both embodiments, however, provide for substantially unimpeded flow of inhalant in a 360° pattern around the animal's head so as to sweep exhaled air away from the animal's nose and mouth.
A yet further embodiment of the invention provides for an inhalant exposure unit having a housing 301 positioned around a central axis having an inlet end and an outlet end. The housing typically forms at least in part a truncated cone. The sides of the truncated cone form an angle θ with respect to the central axis. Typically the angle θ has a value of about 0° to about 60°. A face plate is positioned vertical to the central axis at the outlet end of the housing but not in contact therewith. An annular outlet is formed by the spaced apart relationship of the outlet end and face plate. An outer housing located concentrically around the axis and housing. The outer housing and the housing together form an exhaust passage between them. The outer housing has a back end that corresponds to the inlet end of housing and a front end that aligns with the outlet end of the housing. The front end of the outer housing, however, makes contact with the face plate in a sealing relationship to prevent the loss of inhalant and exhaled breath. The face plate has an axial opening for admitting at least a portion of an animal's head. Typically the animal's head is admitted through the axial opening into the exposure volume around the animals head. The benefits of the invention are obtained by having the flow of inhalant flow past the nostrils and/or mouth of the animal and sweep exhaled breath away from the animal's nostrils or mouth and into the annular outlet. The annular outlet is typically unimpeded by supports and the like so as to not impede the flow of inhalant and exhaled breath. In some embodiments, however, there may be one to several struts or supports (not shown) such as those typically used in the art, that do not substantially interfere with the flow of inhalant and exhaled breath through the annular outlet. The conical shape of housing provides for enhanced flow of inhalant past the animal's head compared to the embodiment that does not use a truncated cone. All embodiments, however, provide for substantially unimpeded flow of inhalant in a 360° pattern around the animal's head so as to sweep exhaled air away from the animal's nostrils and/or mouth. The inhalant and exhaled breath flow into annular outlet and then through the exhaust passage to an outlet. A flow restrictor may be used to further control the flow of inhalant and exhaled breath to the exhaust outlet.
A yet further embodiment of the invention includes an inhalation exposure system for treatment of a patient including an inhalation generator for providing an aerosol or powder; and an inhalation exposure unit having an inlet connected to the inhalation generator that includes
1. a tapered exposure chamber having its inlet at a narrow end and having a port at the wide end of the chamber that accommodates at least a part of a patient's head for breathing from the exposure chamber;
2. an exhaust passage for air flow having an inlet connected to the wider portion of the tapered exposure chamber, and having an outlet, and
3. a flow restrictor in the exhaust passage; and a vacuum unit that provides a vacuum at the outlet of the exhaust passage. Typically the inhalation generator is a nebulizer. The patient to be treated is typically a human or animal.
Broadly the invention provides for an inhalant exposure system for animals that improves the exposure for the animal. The unit provides for low volume displacement providing fast aerosol stabilization and washout. Typically the unit allows near isokinetic sampling that allows the collection of a truer aerosol sample representative of the exposure concentration. The system typically has a flow over muzzle design with exhaust located around the periphery of the animal's neck or head so as to reduce or eliminate aerosol and exhaled air rebreathing. Pressure fluctuation effects and rebreathing of exhaled air on aerosol deliver are also minimized by a vacuum at the exhaust port and a flow restrictor in the exhaust passage. Additionally, the concentric exhaust system provides for more uniform distribution of aerosol in the animal breathing zone prior to exhaust treatment.
The dual unit or multiple unit typically has the ability to expose each animal at different durations based on respiration rate. Typically, each unit has isolation gate valves with fresh air delivery independently for each exposure location. In some embodiments, use of a single sampler for concentration analysis for exposure dose measurement eliminates multiple sample analysis. In other embodiments, pressure and vacuum respiration relief dampers reduce animal respiration effects on aerosol and system flow dynamics and control.
Referring now to
Referring now to
The conical shape the housing 210 provides for enhanced flow of inhalant 121 past the animal compared to the first embodiment that does not use a truncated cone. Both embodiments, however, provide for substantially unimpeded flow of inhalant 121 in a 360° pattern around the animal's head so as to sweep exhaled air away from the animal's nose and mouth.
Referring now to
The face plate has an axial opening 113 for admitting at least a portion of an animal's head 115. Typically the animal's head 115 is admitted through the axial opening 113 into the exposure volume 317. The animal and the animal's head 115 is typically positioned and the size of the axial opening 113 adjusted so that the animal's breathing openings, such as the nostrils 115a and/or mouth 115b, extend into the exposure volume 317 to at least the outlet end 307 of housing 301. Most preferably, to fully realize the benefits of the present invention, the nostrils 115a and/or mouth 115b should extend beyond the outlet end 307 of housing 301 into the treating volume 317. If nose only or mouth only breathing is used, these considerations only apply to the respective breathing opening. The benefits of the invention are obtained by having the flow of inhalant 121 flow past the nostrils 115a and/or mouth 115b of the animal and sweep exhaled breath away from the animal's nostrils or mouth and into the annular outlet 111. The annular outlet 111 is typically unimpeded by supports and the like so as to not impede the flow of inhalant 121 and exhaled breath 122. In some embodiments, however, there may be one to several struts or supports (not shown) such as those typically used in the art, that do not substantially interfere with the flow of inhalant and exhaled breath through the annular outlet 311.
The conical shape of housing 301 provides for enhanced flow of inhalant 121 past the animal's head 115 compared to the first embodiment that does not use a truncated cone. Both embodiments, however, provide for substantially unimpeded flow of inhalant 121 in a 360° pattern around the animal's head so as to sweep exhaled air away from the animal's nostrils 115a and/or mouth 115b. The inhalant 121 and exhaled breath 122 flow into annular outlet 311 and then through the exhaust passage 361 to an outlet 363. A flow restrictor 371 may be used to further control the flow of inhalant 121 and exhaled breath 122 to outlet 363.
In some embodiments, the housing 301 can be shaped as shown by dashed lines 381 to form a unitary structure having one surface 383 substantially parallel to outer housing 351 or any form in between. Flow restrictor 371 typically provides for an opening 373 between the flow restrictor 371 and outer housing 351. This flow restriction provides for more controlled flow of gases in that it is more difficult for the animal's breathing to reverse the flow of gases out of the unit. In some embodiments the flow restrictor 371 may completely close the space between the housing 301 and outer housing 351 and have a plurality of holes (not shown) in the flow to provide controlled flow of inhalant 121 and exhaled breath 122 out of the exhaust passage.
Referring now to
The face plate has an axial opening 113 for admitting at least a portion of an animal's head 115. Typically the animal's head 115 is admitted through the axial opening 113 into the exposure volume 417. The animal and the animal's head 115 is typically positioned and the size of the axial opening 113 adjusted so that the animal's breathing openings, such as the nostrils 115a and/or mouth 115b, extend into the exposure volume 417 to at least the outlet end 407 of housing 401. Most preferably, to fully realize the benefits of the present invention, the nostrils 115a and/or mouth 115b should extend beyond the outlet end 407 of housing 401 into the treating volume 417. If nose only or mouth only breathing is used, these considerations only apply to the respective breathing opening. The benefits of the invention are obtained by having the flow of inhalant 121 flow past the nostrils 115a and/or mouth 115b of the animal and sweep exhaled breath away from the animal's nostrils or mouth and into the annular outlet 111, having an offset distance D1. The annular outlet 111 is typically unimpeded by supports and the like so as to not impede the flow of inhalant 121 and exhaled breath 122. In some embodiments, however, there may be one to several struts or supports (not shown) such as those typically used in the art, that do not substantially interfere with the flow of inhalant and exhaled breath through the annular outlet 411.
The conical shape of housing 401 provides for enhanced flow of inhalant 121 past the animal's head 115 compared to the first embodiment that does not use a truncated cone. Both embodiments, however, provide for substantially unimpeded flow of inhalant 121 in a 360° pattern around the animal's head so as to sweep exhaled air away from the animal's nostrils 115a and/or mouth 115b. The inhalant 121 and exhaled breath 122 flow into annular outlet 411 and then through the exhaust passage 461 to an outlet 463. A flow restrictor 471 may be used to further control the flow of inhalant 121 and exhaled breath 122 to outlet 463. The flow restrictor 471 is typically located D3 units from the exhaust end of the exhaust passage 461. Flow restrictor 471 forms an aperture D2 in the exhaust passage 461. The aperture D2 controls the flow rate of air as further discussed elsewhere herein. Exhaust passage 461 is typically concentric and has a sufficient volume to help damp the pulsating flow of gases produced due to the animal's breathing.
The following examples illustrate various embodiments of the invention. The examples are illustrative only and are not intended to limit the scope of the invention in any way.
For aerosol tests the following biological organisms were used. B. anthracis spores, Ames strain Lot B13, were produced from a single “parent” stock in 1% phenol and sterile water. “Parent” stocks were maintained at temperatures ranging from about 2 to about 8° C. Production was performed according to SOP MREF. X-098 “Production of Bacillus anthracis (hereafter B. anthracis) Spores.
A simulant used was: Polystyrene latex microspheres at sizes of 0.993, 1.992, and 2.92 um from Duke Scientific corp. The simulant is prepared as a suspension in deionized (DI) H2O and reagent grade ethanol.
Referring now to
Aerosol and air then flows to the inlet 573 of the inhalant exposure unit 571 from which the flow is directed to a cone 575 where an animal's mouth and nose are typically placed via port 577. The unused aerosol and air along with exhaled air from the animal flows out of the cone 575 into a concentric inlet 576 to a typically concentric exhaust passage 578. Exhaust passage 578 contains a flow restrictor 579 that controls flow out of the exhaust passage and provides for increased air flow where the animal breathes in the cone 575. This is accomplished by a vacuum applied at an outlet port 581 of the exhaust passage 578. Flow restrictor 579 essentially controls the effects of this applied vacuum in the cone 575. As mentioned earlier the effect of the vacuum and flow restrictor 579 is to increase the speed of air flow at the animal's nose or mouth above the air flow provided by the inflow of air and aerosol to the cone. This has the effect of reducing rebreathing of exhaled air by the animal. Exhaust air flows from outlet port 581 to a valve 583 an optional bypass valve 584 and then to an exhaust pump 585 (with filters 585A) that provides vacuum at the outlet ports 581.
Example 1A laboratory scale inhalant exposure system for providing an inhalant such as an aerosol to animals was built in accordance with the figures. The inhalant exposure system was constructed of Plexiglas™ (although any plastic or metal inert to the test materials will work) and consisted of a 2.54 cm inside diameter tube with a 5.08 cm outside diameter of approximately 56 cm long. The end of the tube was mated with a 10.2 cm long and 5.1 cm inside diameter solid stock of Plexiglas™ with a 10.2 cm outside diameter. The end of the tube was lathed at 30° to form a truncated cone radiating out from the 2.54 cm (1 inch) diameter inner tube, to the 10.2 cm (4 inch) diameter outer tube for the insertion of the animals nose through a rubber dam. A 15.25 cm (6 inch) outside diameter and 12.7 cm (5 inch) inside diameter tube was mounted concentrically with front and back plates around the 10.2 cm (4 inch) diameter tube for exhausting the aerosol from the system. The face plate, located around the animal's nose insertion region, encompassed the cone and was spaced from the cone outlet end by an annular outlet gap of about 1.3 mm. The exhaust outlet increased the acceleration of resident aerosol that passed the animal's nose and/or mouth to facilitate the replenishment of fresh—low residence time biological aerosol in the animal's respiration zone. The aerosol then entered the exhaust passage which contained a flow restrictor which was separated about 3 mm from the outer housing. The flow restrictor acted as an exhaust flow distributor to maintain a consistent exhaust flow around the periphery of the exposure passage and into the exhaust passage before the aerosol was evacuated through an array of three ports located on the back plate of the exhaust passage. The total displacement volume of the inhalant exposure system was approximately 1.4 liters.
The total system flow rate was 10 L/min with 7.5 L/min supplied to the aerosol generator, and 2.5 L/min supplied as dilution air resulting in a flow velocity of approximately 0.3 meters per second. At the tested flow rate, the total system air changes were approximately seven per minute. A Collison 3-jet nebulizer (BGI Inc., Waltham, Mass.) was used to aerosolize the biological agent, B. anthracis (Ames strain), and the biological agent simulant Bacillus globigii (hereafter B. globigii) for testing. Filtered house air was provided to supply a continuous and regulated air source to the Collison nebulizer and for additional dilution air. The Collison nebulizer flow rate was maintained at approximately 7.5 L/min by supplying a continuous and regulated air supply to the Collison at 30 psi, and the flow rate was monitored using a Sierra 0 to 20 L/min mass flow meter (Sierra Instruments, Monterey, Calif.). Dilution airflow was controlled with a needle valve at 2.5 L/min and was monitored using a Sierra 0 to 10 L/min mass flow meter. The Collison nebulizer by-pass airflow was controlled using a needle valve at approximately 7.5 L/min and was monitored using a Sierra 0 to 20 L/min mass flow meter. The bypass flow was used to maintain system pressure and flow stability when the Collison nebulizer was not in use. During testing, the system was maintained under a slight negative pressure of approximately 0.127 cm (0.05 inch) of H2O to avoid contamination of the biological safety cabinet.
A test matrix was developed to characterize the exposure system performance related to inhalant properties such as aerosol concentration stability, aerosol size distribution, aerosol sampler evaluation, and test to test reproducibility.
System concentration stability tests were conducted using fresh 5 mL aliquots from the same B. globigii spore stock for each test. The B. globigii spore stock concentration was 8.08×108 colony forming units per milliliter (cfu/mL) as measured by the spread plate technique and size distribution were measured using a model 3321 Aerodynamic Particle Sizer® Spectrometer (particle sizer) from TSI incorporated (St. Paul, Minn.). The analyzer was designed to accurately measure count and size distribution of particles with aerodynamic diameters in the range of 0.5 to 20 μm.
For stability testing, particle sizer samples were taken during the entirety of each test, and included measuring the post generation concentration decline until the system was purged of aerosol.
Referring now to
The particle size analyzer was programmed to pull sequential samples from the exposure system for 30 seconds starting at the initiation of aerosol generation with a 30 second delay between samples. A total of fourteen particle sizer samples were collected. This included measuring the post generation concentration decline for four minutes after the 10-minute aerosol generation period. The flow rate through the Collison nebulizer was maintained at 7.5 L/min with a dilution airflow rate of 8.5 L/min for a total system flow rate of 16.0 L/min. These flow rates were used to simulate system operation parameters used during actual exposure testing.
Testing showed that the current aerosol system maintains a peak aerosol concentration after about a 3 to about 4 minute ramp-up time.
Aerosol System Particle Size TestingTwelve individual 5 minute inhalation exposure system tests were conducted using a fresh 5 mL aliquot from the same B. globigii spore stock with a concentration of 8.08×108 colony forming units per milliliter (cfu/mL). Nine 10 minute tests were also conducted using a fresh 5 mL aliquot from the same B. anthracis spore stock (Lot number Ames-B8) with a concentration of 1.0×107 colony forming units per milliliter (cfu/mL). Particle sizer samples were taken for a duration of 30 seconds at the midpoint of each B. globigii and B. anthracis test to compare test to test stability and/or variation of the particle size distribution.
Data obtained from testing the inhalant exposure system shows promising results with applications for bioaerosol studies in the primate and rabbit models. The aerosol concentration stability test results from
The inhalation exposure system has shown superiority by having a low displacement volume, a rapid development to peak aerosol concentration, a stable peak aerosol concentration, a rapid decay of agent, sampling directly from the aerosol stream for accurate aerosol concentration determination, decreased aerosol residence time, and the potential for decreasing the aerosol exposure duration that conserves biological agent.
Referring now to
The length of tube 930 is any that provides a good flow aerosol flow path, distribution to sensing instruments and proper delivery to the inlet 933 of dual tubes 935A, 935B that provide flow to inlets 973A, 973B of the dual inhalant exposure unit 971. A differential pressure gauge 532 is typically used to monitor pressure in tube 930. Vacuum and pressure relief vessels 533 along with associated filters 534 (e.g. HEPA filters) may be used to control pressure in the tube 930. A sample collector such as an impinger 541 may connected to the tube 930 to collect aerosol particles. A critical orifice 543, along with vacuum gauge 545, valve 548 and a vacuum pump 549 along with filters 549A may be used to aid in collecting the samples. In one embodiment the critical orifice provides a flow of air of 2 L/min. An optional aerodynamic particle sizer 552 connected to the tube 530 may be used with a computer 553 to aid in monitoring and controlling particle size.
Aerosol and air then flows to the inlet 933 two tubes 935A, 935B of the dual portion of inlet 573 of the inhalant exposure unit 571 from which the flow is directed to a cones 595A, 975B where an animal's mouth and nose are typically placed via ports 977A, 977B. The unused aerosol and air along with exhaled air from the animal flows out of the cone 975A, 975B into a concentric inlet 576A, 975B to a typically concentric exhaust passage 978A, 978B. Exhaust passage 978A, 978B contains a flow restrictor 979A, 979B that controls flow out of the exhaust passage and provides for increased air flow where the animal breathes in the cone 975A, 975B. This is accomplished by a vacuum applied at an outlet port 981A, 981B of the exhaust passage 978A, 978B. Flow restrictor 979A, 979B essentially controls the effects of this applied vacuum in the cone 975A, 975B. As mentioned earlier the effect of the vacuum and flow restrictor 979A, 979B is to is increase the speed of air flow at the animal's nose or mouth above the air flow provided by the inflow of air and aerosol to the cone. This has the effect of reducing rebreathing of exhaled air by the animal. Exhaust air flows from outlet port 981A, 981B to a mass flow controller 983A, 983B then to an optional bypass valve 584, or to an exhaust pump 585 (with filters 585A) that provides vacuum at the outlet ports 581.
Additionally, the dual tubes 935A, 935B have control valve 937A, 937B that controls the flow of air and aerosol to the animal. A bypass filter 939A, 939B is used to supply air flow to an animal without aerosol when the valve 937A, 937B is turned off. These valves are also referred to as isolation valves.
Example 2 Multiple Animal Inhalation Exposure SystemThe multiple inhalation exposure system (
Referring now to
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Referring now to
Aerosol Challenge (Nebulizer) Suspension Enumeration: The challenge spore suspensions (B. anthracis) were prepared by diluting the stock suspension to a targeted concentration. The challenge spore suspension was enumerated by serial dilution of the challenge suspension by spreading 0.1 mL on each of five tryptic soy agar plates for three different dilutions. The tryptic soy agar plates were placed in a secondary container and incubated at 37° C. for 16-24 hours. After the incubation period, the number of colonies on each plate was counted. Each concentration was determined by the spread plate method.
Example 4As tested, the total system flow rate for all testing was 20 L/min, resulting in a flow velocity of approximately 0.66 meters per second through the main delivery tube, and a velocity of 0.51 meters per second through each section of the Tygon aerosol delivery tubing. A total of 2.5 liters of the total flow is sampled from the main aerosol delivery tube before the aerosol is diverted to the two Tygon tubes and delivered to the exposure units. The diverted air flow supplied to each exposure unit is maintained at a flow rate of approximately 8.75 L/min using mass flow controllers (Sierra Instruments, Monterey, Calif.) for control of the exhaust flow of each exposure unit. At the tested flow rate, the total system air changes are approximately sixteen per minute.
Example 5Simulant Testing: The objective of this testing was to characterize the exposure system and assess individual parameters of the exposure system which include aerosol homogeneity, concentration ramp up, concentration stability, and decline, as well as aerosol transport losses, sample measurement to exposure location concentration variation, exposure location to exposure location variation, and sampling system collection efficiencies. To characterize these system parameters, individual polystyrene latex microsphere standards were prepared at sizes of 0.993, 1.992, and 2.92 um suspended in solutions of deionized sterile water and reagent grade ethanol. To accurately characterize and assess the exposure system, two particle sizers TSI inc. St. Paul, Minn. were used in tandem sampling simultaneously at separate locations in the exposure system for comparative count concentration measurements. The particle sizer's were concentration count rate correlated with each polystyrene latex suspension size prior to all characterization testing. This was performed to measure the count concentration measurement variation between the two instruments and to correct for concentration count and mass concentration measurement results obtained from characterization testing. The particle sizers were correlated by aerosolizing each individual size suspension into a small plenum using a Westmed Vixone™ disposable nebulizer, and sampling simultaneously with both instruments from the same location at the same sample flow rate from the plenum.
For exposure system homogeneity characterization tests, one particle sizer was utilized to sample from the impinger sample location (reference) and the other particle sizer was used to alternately sample from both exposure locations. The particle sizer's were synchronized to sample simultaneously from both locations to measure the variation in aerosol count and mass concentration for each polystyrene latex microsphere size. To generate the challenge aerosol for each polystyrene latex microsphere size, an individual Vixone nebulizer was used for each suspension size to avoid suspension cross contamination. The Vixone nebulizers were operated in the range of 5 L/min with additional aerosol dilution air supplied to the system to obtain a total flow of 20 L/min. During testing, the system was maintained under a slight negative pressure of approximately 0.127 cm (0.05 inch) of H2O to avoid contamination of the test environment.
A modified Microbiological Research Establishment type three-jet Collison nebulizer (BGI, Waltham, Mass.) with a precious fluid jar was used to aerosolize the biological agent, B. anthracis (Ames strain) from a water suspension. B. anthracis spores with a stock concentration of 6.5×108 colony forming units per milliliter (cfu/mL) as measured by the spread plate technique.
Air was supplied to the aerosol system by an in-house system filtered through a high efficiency particulate (HEPA) capsule filter. A Collison 3-jet nebulizer (BGI Inc., Waltham, Mass) was used to aerosolize the biological agent, B. anthracis (Ames strain). Filtered house air was provided to supply a continuous and regulated air source to the Collison nebulizer and for additional dilution air. The Collison nebulizer flow rate was maintained at approximately 7.5 L/min by supplying a continuous and regulated air supply to the Collison at 27 psi, and the flow rate was monitored using a Sierra 0 to 20 L/min mass flow meter (Sierra Instruments, Monterey, Calif.). Dilution airflow was controlled with a needle valve at 12.5 L/min and was monitored using a Sierra 0 to 20 L/min mass flow meter. The Collison nebulizer by-pass airflow was maintained at approximately 7.5 L/min and was controlled using a Sierra 0 to 20 L/min mass flow controller. The bypass flow was used to maintain system pressure and flow stability when the Collison nebulizer was not in use. Air flow delivered to each exposure unit was maintained at a flow rate of approximately 8.75 L/min using mass flow controllers (Sierra Instruments, Monterey, Calif.) for control of the exhaust flow of each exposure unit. During testing, the system was maintained under a slight negative pressure of approximately 0.127 cm (0.05 inch) of H2O to avoid contamination of the biological safety cabinet.
System concentration stability tests were conducted with B. anthracis spores with a stock concentration of 6.5×108 colony forming units per milliliter (cfu/mL) as measured by the spread plate technique. Particle counts and size distribution were measured using a model 3321 Aerodynamic Particle Sizer® Spectrometer (particle sizer) from TSI incorporated (St. Paul, Minn.). The analyzer is designed to accurately measure count and size distribution of particles with aerodynamic diameters in the range of 0.5 to 20 μm. The particle sizer analyzer was programmed to pull sequential samples from the exposure system with no time delay between samples. This sequenced sampling was performed to measure the count rates at specific time intervals to determine when exposure system concentration stability is achieved. For stability testing, particle sizer samples were taken during the entirety of each test, and included measuring the post generation concentration decline until the system was purged of aerosol.
Midget Impingers model 7531-25 (Ace Glass Incorporated, Vineland, N.J.). For each test, three midget impinger were filled with 10 mL of sterile water from Sigma (St. Louis Mo.). The samplers were used to collect a representative fraction of the challenge aerosol from the midget impinger sample location as well as from exposure units 1, and 2. The impingers were operating simultaneously during each B. anthracis challenge test to measure variation in colony forming unit (cfu) concentration from location to location.
Five ten-minute tests were performed to evaluate system bioaerosol concentration variation. The samples were pulled from the exposure system during the entirety of an aerosol challenge test. The B. anthracis spore concentration collected by the samplers was measured by the spread plate technique.
For each test, the Collison nebulizer was filled with a fresh 8 mL aliquot of the B. anthracis stock suspension. The flow rate through the Midget impingers (3) sampling from the impinger sample port as well as exposure unit one and two, were each controlled at a flow rate of 2 L/min with a flow calibrated critical orifice from Lenox Laser (Glen Arm, Md.), by maintaining a negative pressure of 45.72 cm (18 inch) of Hg using a ⅕ hp vacuum pump (Gast Manufacturing, Benton Harbor, Mich.). Table 2 shows the sampler cfu collection data obtained for each test and exposure unit to exposure unit percent difference in cfu concentration.
Data obtained from testing the new inhalant exposure system showed promising results with applications for bioaerosol studies in the primate and rabbit models. The aerosol homogeneity test results from
Bioaerosol aerosol delivery efficiencies from data in
The B. anthracis bioaerosol stability data
The new aerosol system has shown superiority over a currently used aerosol system by having a lower displacement volume, a rapid development to peak aerosol concentration, a stable peak aerosol concentration, a rapid decay of agent, sampling directly from the aerosol stream for accurate aerosol concentration determination, decreased aerosol residence time, and the potential for decreasing the aerosol exposure duration. The ability to expose two or more animal models of the same or different species, and the use of a single sampler for the quantification of cfu's delivered to the animals will also conserve biological agent and personnel hours.
Example For Flow Rate CalculationReferring now to
Flow=Q.
Exposure system flow Q at the main tube=20 L/min, Impinger Q=2.0 L/min, APS Q=0.5 L/min.
Exhaust flow total to animal Q=17.5 L/min÷2=8.75 L/min
Impinger and APS flows were removed from the calculation since the flow of gas to these units does not go to the animal; division is by two when there are two animals exposed simultaneously.
The exposure system gas flow Q to each animal is 8.75 L/min
Q=(8.75 L/min×0.001 m3/L)÷60 sec/min=1.46×10−4 m3/sec
Area of tube=n (pi) (0.0254 m2)÷4=5.06×10−4 m2
since Vel=Q/Area (1.46×10−4 m3/sec)÷5.06×10−4 m2
Vel=0.29 m/sec at the animals nose or mouth
This is the velocity of gas flow past the animal's nose or mouth and indicates that adequate flow is being provided to an animal such as a mouse or similar small animal to prevent rebreathing.
The aperture at D2 provides for increased exhaust velocity at the point where the gas has passed the animal's nose or mouth. This is accomplished by having a negative pressure applied at the exhaust 477 and appropriate sizing of aperture D2. D1 is assumed to be large for this and can be ignored. However in some embodiments the aperture D1 may be acting as a flow accelerator by itself if there is not aperture D2 further down the flow path.
Calculation for aperture D2 exhaust velocity
Aperture width—1.3 mm×2=2.6 mm
Area of aperture=n r2 outer−n r2inner
Outer diameter=4 inches×25.4 mm/inch=1.01.6 mm=0.1016 m thus r=0.0508 m
Inner diameter=0.1016 m−0.0026 m=0.099 m thus r=0.0495 m
Area of aperture D2=n (0.0508 m)2−n (0.0495)2=0.0004 m2
Thus the gas flow velocity at the aperture is
V=Q/A=1.46×10−4 m3/sec÷4.0×10−4 m2=0.365 m/sec
Thus the gas flow rate is accelerated by the aperture.
If D1 is the flow constrictor than it would be used in the calculation, however the preferred flow constrictor is at D2.
While the forms of the invention herein disclosed constitute presently preferred embodiments, many others are possible. It is not intended herein to mention all of the possible equivalent forms or ramifications of the invention. It is to be understood that the terms used herein are merely descriptive, rather than limiting, and that various changes may be made without departing from the spirit of the scope of the invention.
Claims
1. An inhalant exposure unit comprising:
- a. a housing concentrically positioned around a central axis having an inlet and an outlet;
- b. a face plate positioned vertically to the central axis at the outlet of the housing, wherein the outlet of the housing and a surface of the face plate are separated by a distance D1 comprising an annular outlet between the outlet of the housing and the surface of the face plate; and
- d. an opening in the face plate for admitting at least a portion of an animal's head into the housing.
2. The inhalant exposure unit according to claim 1, wherein at least a portion of the housing comprises a truncated cone having a surface at an angle θ with respect to the central axis, wherein the smaller end of the cone comprises an inlet, and the outlet is at the larger end of the cone.
3. The inhalant exposure unit according to claim 1 or 2, comprising an outer housing concentrically located around the housing wherein the outer housing and the housing form an exhaust passage connected to the annular outlet for exhausting inhalant and an animal's exhaled breath.
4. The inhalant exposure unit according to claim 3, wherein a flow restrictor is located in the exhaust passage.
5. The inhalant exposure unit according to claim 3, wherein the flow restrictor is located concentrically within the exhaust passage and forms an annular exhaust orifice.
6. The inhalant exposure unit according to claim 3, wherein the exhaust orifice has an annular outlet of distance D2.
7. The inhalant exposure unit according to claim 3, wherein the flow restrictor is located a distance D5 from the exhaust.
8. The inhalant exposure unit according to claim 1, wherein the annular outlet comprises an annular gap without a support across the gap.
9. The inhalant exposure unit according to claim 1, wherein annular outlet comprises an annular gap with a least one spaced support across the gap.
10. The inhalant exposure unit according to claim 1, wherein the annular gap comprises a distance D1.
11. The inhalant exposure unit according to claim 1, wherein an essentially flexible seal located concentrically with respect to the central axis contacts at least a portion of the face plate, and has a central orifice for admission of an animal's head or muzzle.
12. The inhalant exposure unit according to claim 3, wherein an outlet port at the exhaust passage comprises a plurality of holes.
13. The inhalant exposure unit according to claim 3, wherein the flow restrictor comprises an annular ring that blocks a portion or all of the exhaust passage, and has a plurality of holes.
14. The inhalant exposure unit according to claim 2, wherein the angle θ ranges from about 0° to about 50°.
15. The inhalant exposure unit according to claim 14, wherein the angle θ ranges from about 10° to about 40°.
16. The inhalant exposure unit according to claim 1 or 2, wherein the unit Has a unitary structure.
17. The inhalant exposure unit according to claim 2, wherein the outer housing, housing, an optional inlet tube, and truncated cone are essentially concentric about the central axis.
18. A method for testing an animal with an inhalant comprising;
- a. providing an inhalant exposure unit according to claim 1;
- b. placing an animal's head or muzzle within the opening of the face plate; and
- c. flowing an inhalant into the inlet.
19. A multiple inhalant exposure system comprising:
- a. two or more inhalant exposure units according to claim 1 or 2; and
- b. a distributor having an inlet for inhalant and two or more distribution tubes, wherein each tube has an outlet operationally connected to the inlet of each inhalation exposure unit.
20. An inhalation exposure system comprising;
- a. an inhalant generator;
- b. a tube with an inlet and an outlet, wherein the inlet is connected to the output of the inhalant generator; and
- c. an inhalation exposure unit according to claim 1 or 2, wherein the inlet of the inhalation exposure unit is connected to the tube outlet.
21. An inhalation exposure system for treatment of a patient comprising;
- a. an inhalation generator for providing an aerosol or powder;
- b. an inhalation exposure unit having an inlet connected to the inhalation generator comprising: 1. a tapered exposure chamber having a narrow and a wide end, with the inlet at the narrow end of the chamber and having a port at the wide end of the chamber that accommodates at least a part of a patient's head for breathing from the exposure chamber; 2. an exhaust passage, having an inlet connected to the wide portion of the tapered exposure chamber, and having an outlet; 3. a flow restrictor in the exhaust passage; and
- c. a vacuum unit that provides a vacuum at the outlet of the exhaust passage.
22. The inhalation exposure system according to claim 21, wherein the inhalation generator is a nebulizer.
23. The inhalation exposure system according to claim 21, wherein the patient to be treated is a human or animal.
24. The inhalation exposure system according to claim 21, wherein the vacuum unit is a pump.
25. The inhalation exposure system according to claim 21, wherein the exhaust passage and its inlet is substantially concentric to the chamber.
Type: Application
Filed: Sep 29, 2006
Publication Date: Jan 15, 2009
Inventors: Roy Edmund Barnewall (Columbus, OH), Richard Scott Tuttle (Overland Park, KS)
Application Number: 12/088,454
International Classification: A61M 16/00 (20060101); A01K 1/03 (20060101);